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Small Intestine Physiology
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Small Intestine Physiology
Small Intestine Physiology
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1
Question
What initiates digestion in the stomach before small intestine absorption?
Answer
Breaking solids to particles ≤1 mm
2
Question
What is the primary role of the small intestine in digestion?
Answer
Absorbing almost all dietary components
3
Question
How is water absorbed in the small intestine?
Answer
Simple diffusion and osmotic pressure from Na+, glucose, amino acid transport
4
Question
Daily water volume entering small intestine and reaching colon?
Answer
∼8−10 L enter, ≤500 mL reach colon
5
Question
Mechanism of Na+ absorption in small intestine?
Answer
Active transport through basolateral membranes
6
Question
How is Cl− absorbed in the upper small intestine?
Answer
Passive diffusion
7
Question
Indirect reabsorption mechanism of HCO3− in small intestine?
Answer
H+ secretion forms CO2 and water; CO2 absorbed
8
Question
What enhances Ca2+ absorption in duodenum/jejunum?
Answer
Acid environment, Vitamin D, parathyroid hormone
9
Question
Site and process of iron absorption in small intestine?
Answer
Duodenum as heme or nonheme by active process
10
Question
Storage forms of absorbed iron in the body?
Answer
Ferritin or bound to transferrin in plasma
11
Question
How are fat-soluble vitamins (A, D, E, K) absorbed?
Answer
Carried in mixed micelles, transported via chylomicrons in lymphatics
12
Question
Absorption mechanism of Vitamin C and B1?
Answer
Active transport with sodium-coupled mechanisms
13
Question
How is Vitamin B6 absorbed in the small intestine?
Answer
Simple diffusion in proximal intestine
14
Question
Primary site and mechanism of Vitamin B12 absorption?
Answer
Terminal ileum; binds Intrinsic Factor, uptake by specific receptors
15
Question
What is peristalsis in small intestine motility?
Answer
Contractions passing aborally at 1−2 cm/sec to move chyme
16
Question
Initiator of contractions in fed state of small intestine?
Answer
Pacesetter potentials originating in duodenum
17
Question
Fasted state motility pattern in small intestine?
Answer
Migrating Myoelectric Complex (MMC) every 75−90 minutes
18
Question
Neural control excitatory effect on small intestine motility?
Answer
Parasympathetic vagal cholinergic fibers
19
Question
Hormonal initiator of phase III MMC in small intestine?
Answer
Motilin plasma levels peak
20
Question
Largest endocrine organ in the body?
Answer
Small bowel
21
Question
Roles of GI hormones in small intestine function?
Answer
Control secretion, absorption, motility; trophic effects on mucosa/pancreas
22
Question
Primary signaling receptors for GI hormones?
Answer
G protein-coupled receptors using cAMP, Ca2+, cGMP
23
Question
Receptor type for growth factors like EGF, IGF, PDGF?
Answer
Tyrosine kinase receptors affecting cell growth/differentiation
24
Question
Major immunological barrier of small intestine?
Answer
Single-layer epithelium with extensive lymphoid tissue
25
Question
Key antigenic sites in small intestine lymphoid tissue?
Answer
Peyer patches, lamina propria cells, Paneth cells, intraepithelial lymphocytes
26
Question
Function of Peyer patches in GALT?
Answer
Unencapsulated lymphoid nodules; M cells sample intraluminal antigens
27
Question
Composition of lamina propria in small intestine?
Answer
∼60% T cells, B cells, plasma cells, macrophages
28
Question
Primary immunoglobulin synthesized in lamina propria B cells?
Answer
Immunoglobulin A (IgA)
29
Question
Location and role of Paneth cells in small intestine?
Answer
Base of crypts; release antimicrobial factors protecting stem cells
30
Question
Function of intraepithelial lymphocytes (IELs)?
Answer
Cytolytic functions for immunosurveillance between epithelial cells